_indexed_ iteration using opApply or range

[spir]

On Sun, 12 Dec 2010 21:15:00 +0100
"Simen kjaeraas" <simen.kjaras at gmail.com> wrote:

> The trick to ranges is that they modify themselves. For a simple array  
> wrapper
> range this may be a way:
> 
> struct wrapper( T ) {
>      T[] data;
>      void popFront( ) {
>          data = data[1..$];
>      }
>      ref T front( ) {
>          return data[0];
>      }
>      bool empty( ) {
>          return data.length == 0;
>      }
> }
> 
> Feel free to ask if you wonder about anything specific.

Thank you, Simen. 2 comments:

(1) In my case, I do not want to modify the range (actually the private collection), because the type is not only about beeing a range (~ provide iteration). So that I defined the range methods, using a private 'rangeIndex slot', as (the type also maintains a 'length' slot):

    private uint rangeIndex;
    @property void popFront () {
        // (re)start...
        if (this.rangeIndex >= this.length)
            this.rangeIndex = 0;
        // ...or move on
        else
            ++ this.rangeIndex;
    }
    @property bool empty () {
        return (this.rangeIndex >= this.length);
    }
    @property T front () {
        return this.stacks[this.rangeIndex];
    }

Note that this also enables a restarting feature :-)

(2) How then can I introduce indexed iteration (or more generally iteration with more than one parameter to the block), using ranges? The blocking (!) point is there is no way for front() to return a several multiple results.
I can cheat using a tuple or struct, but D won't understand and unpack it for the user :-) Sure, the user may know I return a pack, but...


Denis
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vit esse estrany ☣

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